Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session H8: Grain-Scale to Continuum Modeling II |
Hide Abstracts |
Chair: Darby J Luscher, Los Alamos National Laboratory Room: Grand Ballroom C |
Tuesday, July 11, 2017 9:15AM - 9:30AM |
H8.00001: Numerical study on tailoring the shock sensitivity of TATB-based explosives using mesostructural features H. Keo Springer Advanced manufacturing techniques offer control of explosive mesostructures necessary to tailor its shock sensitivity. However, structure-property relationships are not well established for explosives so there is little material design guidance for these techniques. The objective of this numerical study is to demonstrate how TATB-based explosives can be sensitized to shocks using mesostructural features. For this study, we use LX-17 (92.5\%wt TATB, 7.5\%wt Kel-F 800) as the prototypical TATB-based explosive. We employ features with different geometries and materials. HMX-based explosive features, high shock impedance features, and pores are used to sensitive the LX-17. Simulations are performed in the multi-physics hydrocode, ALE3D. A reactive flow model is used to simulate the shock initiation response of the explosives. Our metric for shock sensitivity in this study is run distance to detonation as a function of applied pressure. These numerical studies are important because they guide the design of novel energetic materials. LLNL-ABS-724986. [Preview Abstract] |
Tuesday, July 11, 2017 9:30AM - 9:45AM |
H8.00002: Detection of plasticity mechanisms in an energetic molecular crystal through shock-like 3D unidirectional compressions : A Molecular Dynamics study Paul Lafourcade, Christophe Denoual, Jean-Bernard Maillet TATB crystal structure consists in graphitic-like sheets arranged in the a-b plane where a, b and c define the edge vectors of the unit cell. This type of stacking provides the TATB monocrystal very anisotropic physical, chemical and mechanical properties. In order to explore which mechanisms are involved in TATB plasticity, we use a Molecular Dynamics code in which the overall deformation is prescribed as a function of time, for any deformation path. Furthermore, a computation of the Green-Lagrange strain tensor is proposed, which helps reveal various defects and plasticity mechanisms. Through prescribed large strain of shock-like deformations, a three-dimensional characterization of TATB monocrystal yield stress has been obtained, confirming the very anisotropic behavior of this energetic material. Various plasticity mechanisms are triggered during these simulations, including counter intuitive defects onset such as gliding along transveral planes containing perfect dislocations and twinning. Gliding in the a-b plane occurs systematically and does not lead to significant plastic behavior, in accordance with a previous study on dislocation core structures for this plane, based on a coupling between the Peierls-Nabarro-Galerkin method and Molecular Dynamics simulations. [Preview Abstract] |
Tuesday, July 11, 2017 9:45AM - 10:00AM |
H8.00003: Simulations and Experiments of Dynamic Granular Compaction in Non-ideal Geometries Michael Homel, Eric Herbold, John Lind, Ryan Crum, Ryan Hurley, Minta Akin, Darren Pagan Accurately describing the dynamic compaction of granular materials is a persistent challenge in computational mechanics. Using a synchrotron x-ray source we have obtained detailed imaging of the evolving compaction front in synthetic olivine powder impacted at $300-600m/s$. To facilitate imaging, a non-traditional sample geometry is used, producing multiple load paths within the sample. We demonstrate that (i) commonly used models for porous compaction may produce inaccurate results for complex loading, even if the $1-D$, uniaxial-strain compaction response is reasonable, and (ii) the experimental results can be used along with simulations to determine parameters for sophisticated constitutive models that more accurately describe the strength, softening, bulking, and poroelastic response. Effects of experimental geometry and alternative configurations are discussed. Our understanding of the material response is further enhanced using mesoscale simulations that allow us to relate the mechanisms of grain fracture, contact, and comminution to the macroscale continuum response. Numerical considerations in both continuum and mesoscale simulations are described. [Preview Abstract] |
Tuesday, July 11, 2017 10:00AM - 10:15AM |
H8.00004: Multiscale Deformation behavior of polymer bonded explosives subjected to intermediate velocity impact Suraj Ravindran, Peter Malchow, Addis Tessema, Addis Kidane We present a multiscale experimental investigation of polymer bonded sugar (PBS), a mechanical simulant of PBX, subjected to impact loading. The experiments are conducted by shooting a projectile onto the PBS specimen at an impact velocity of 56m/s using modified split Hopkinson bar apparatus. Images at two different scales are captured for macroscale (continuum) and mesoscale (local) deformation measurement during the loading at a rate of 2 million frames/second. The local deformation measurement is conducted using a newly developed high speed-high spatial resolution image based diagnostic technique. Based on the macroscale full-field information, the compaction wave velocity and the compaction wave thickness are calculated. Further the stress in front and behind the compaction front is calculated. It is observed that the compaction wave width is not constant, instead, increases as it propagates towards the other end. The change in compaction width could be due to energy dissipation during deformation. The meso-scale measurement provided insight into what might have happened during wave propagation. Deformation such as grain fracture, plastic deformation, and relative sliding of crystal have been observed and could have contributed to the energy dissipation. [Preview Abstract] |
Tuesday, July 11, 2017 10:15AM - 10:45AM |
H8.00005: Modeling the nonlinear finite compression response of crystalline solids with generalized Finsler-geometric continuum mechanics Invited Speaker: John Clayton A continuum theory based on Finsler differential geometry [1] and phase field dynamics is presented. A director component of pseudo-Finsler space is treated as an order parameter; volume dependence obeys a conformal transformation. Applications demonstrate predictive capabilities with little, if any, parameter fitting. \\ The first application addresses shock compression of magnesium along the c-axis. The order parameter quantifies pyramidal slip and dislocations. Jump conditions for planar shocks are solved. Unlike usual crystal plasticity models [2], no flow rule is required, with slip found from order parameter equilibrium [1]. \\ The second application addresses shear and compression of boron carbide. Two order parameters enter a generalized Finsler state vector: the first accounts for twinning and/or amorphization, the second for fracture. Numerical solutions elucidate failure kinetics, and mesoscale simulations probe effects of polycrystal morphology. \\ \\ $[1]$ J.D. Clayton. Finsler geometry of nonlinear elastic solids with internal structure. Journal of Geometry and Physics 112:118-146, 2017. \\ $[2]$ J.D. Clayton and D.L. McDowell. A multiscale multiplicative decomposition for elastoplasticity of polycrystals. International Journal of Plasticity 19:1401-1444, 2003. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700